The present invention relates to an antenna device for a hand-portable radio communication unit, in particular a mobile telephone, including a casing, in which a ground plane means having at least one edge is disposed. The antenna device comprises first and second radiating elements carried by support means, and said first and second radiating elements being tuned to different resonant frequencies.
Such an antenna device is disclosed in the international patent application PCT/SE97/01046 (Allgon AB), wherein an embodiment shown in FIG. 3A includes first and second radiating elements in the form of flat meander-configured elements disposed on a flexible film carrier which is bent into a cylindrical shape. The cylindrical support means with the first and second meander elements are arranged as a cylindrical or somewhat conical element projecting upwards from a top portion of the telephone casing adjacent to a corner thereof. As is also generally known per se, the known antenna device includes a whip or rod antenna element, which is mechanically supported centrally in the projecting element and is movable between an operative extended position and a non-operative retracted position.
Thus, the previously known antenna device is basically located outside the casing as indicated above.
With this background, a main object of the present invention is to provide a compact antenna device which can be disposed substantially inside the casing so as to avoid any outwardly projecting sleeve or conical member, except for a possible extendable whip or rod antenna element. It is also desirable to make the whole radio communication unit or mobile telephone compact by such a measure.
Another object is to provide an antenna device having a low weight.
Still another object is to provide an antenna element having a satisfactory efficiency and bandwidth for each frequency in spite of a low volume of the device. The performance should be at least as good as for a conventional, stationary helix antenna.
Still another object is to provide a built-in antenna device, which can be manufactured in large series at low costs.
Still another object is to provide an antenna element also provided with a rod having a reduced total length (for a given radiating length).
According to a first aspect of the invention the main object stated above is achieved for an antenna device having the features stated as first and second radiating elements carried by a support means. Thus, the first and second radiating elements, each being tuned to a specific resonant frequency, are disposed in a compact arrangement on a support means, which is adapted to be mounted with the first and second radiating elements located in proximity of, i.e. adjacent to, one or two edges of the ground plane means so as to be confined entirely in the casing. The two radiating elements preferably extends with their longitudinal axes substantially in parallel to said one or two edges.
In a preferred embodiment, wherein the casing is shaped substantially as an elongated box with the antenna device located adjacent to an end port ion thereof, the support means, together with the first and second radiating elements, is dimensioned so as to extend transversely between the opposite longer sides of the elongated box constituting the casing.
Thus, the first and second radiating elements are confined entirely in the casing. However, it is possible to combine these first and second radiating elements with a third radiating element in the form of a whip or a rod, which is connectable to a feed point of the radiating elements so as to be coupled electrically in parallel to the first and second radiating elements. Preferably, the rod is movable between an operative extended position, located at least partially outside the casing, and a retracted position, located substantially inside the casing.
The first and second radiating elements are preferably constituted by flat substantially meander-configured elements or flat elongated substantially straight elements, whereby the weight of the antenna device can be kept very low. However, it is also possible to use helical elements.
In one preferred embodiment said first and second elements are located on mutually perpendicular sides of said support means.
These and other preferred features of the invention are stated in the dependent claims 2-19 and will appear from the detailed description below.
According to a second aspect of the invention, the main object stated above is achieved for an antenna of device having the features stated in any one of claims 20-22, i.e. with a rod element in combination with at least one internal radiating element having multiple turns.
This geometry may generally allow an arrangement wherein the rod element and the internal element have a relatively small electromagnetic interaction.
The invention also concerns a radio communication unit comprising an antenna device as defined in any one of the claims 1-22.